The overall objective of this project is to gain a greater understanding of the factors which regulate mitochondrial biogenesis. Although mitochondria have the ability to synthesize less than 10% of their total proteins, the 8-10 hydrophobic proteins made within the mitochondria are essential for the formation of a functional respiratory chain and ATP synthesizing complex. This project proposes to investigate the mechanisms which control the synthesis of mitochondrial proteins at the two different intracellular sites. Specifically, possible controls at both the transcriptional and translational level will be investigated by the use of polysomes isolated from yeast mitochondria. Mitochondrial messenger RNAs will be characterized as will be the nature of the nascent chains present on the polysomes. In conjunction with these studies, the assembly of cytochrome b, a product of mitochondrial protein synthesis, into complex III of the respiratory chain will be studied by use of specific mutants as well as antibodies to the purified enzyme. These proposed experiments should help elucidate how the mitochondrial membrane is assembled. Furthermore, it should provide synthesis within mitochondria by events occurring in the cytoplasm.